In a rolling process of a flat-rolled metal material, it is very important to roll a sheet material in a form free from camber, or in a form not having bend in the left-right direction, in order to avoid not only a plane shape defect and a dimensional accuracy defect of the rolled material but also to avoid sheet pass troubles such as a zigzag movement and a tail crash.
Incidentally, to simplify expressions, the operator side and the driving side of the rolling mill, as the right and left sides when the rolling mill is seen from the front of the rolling direction, will be called “right and left”, respectively.
To cope with such problems, Japanese Unexamined Patent Publication (Kokai) No. 4-305304 discloses a camber control technology that arranges devices for measuring the lateral positions of the rolled material on the entry and exit sides of the rolling mill, calculates the camber of the rolled material from the measured values and regulates the position of an edger roll, arranged on the entry side of the rolling mill, to correct the camber.
On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 7-214131 discloses a camber control technology that controls a left-right difference of roll gap of the rolling mill, that is, reduction leveling, on the basis of a left-right difference in edger roll loads provided on the entry and exit sides of the rolling mill.
Japanese Unexamined Patent Publication (Kokai) No. 2001-105013 discloses a camber control technology that analyzes actual measurement values of a left-right difference of rolling loads and controls a left-right difference of roll gap, that is, reduction leveling, or positions of side guides.
Japanese Unexamined Patent Publication (Kokai) No. 8-323411 discloses a method that conducts camber control by restricting a rolled material by an edger roll and a side guide on the entry side and a side guide on the exit side.
However, the invention relating to the camber control technology by the lateral position measurement of the rolled material described in Japanese Unexamined Patent Publication (Kokai) No. 4-305304 is basically directed to the correction of the camber that has already occurred and cannot substantially, in advance, prevent the occurrence of a camber.
According to the invention relating to the camber control technology based on the edger roll load left-right difference on the entry and exit sides of the rolling mill and described in Japanese Unexamined Patent Publication (Kokai) No. 7-214131, it is difficult to acquire good control accuracy when the camber already exists in the rolled material on the entry side because the camber operates as disturbance to the edger roll load difference on the entry side. The edger roll on the exit side must be saved back at the time of passing of the distal end of the rolled material in order to avoid impingement, and it is difficult, too, to conduct camber control from the distal end of the rolled material.
According to the invention relating to the camber control technology based on the rolling load left-right difference described in Japanese Unexamined Patent Publication (Kokai) No. 2001-105013, the method of estimating the camber from the left-right difference of the rolling load has extremely low accuracy and is not practical when the sheet thickness of the rolled material on the entry side is not uniform in the sheet width direction or when the temperature distribution of the rolled material is not uniform in the sheet width direction.
In the invention relating to the camber control by using the edger roll on the entry side, the side guide on the entry side and the side guide on the exit side and described in Japanese Unexamined Patent Publication (Kokai) No. 8-323411, the exit side camber can be made zero if the side guide on the exit side can completely restrict the rolled material on the exit side. However, because the side guide on the exit side must be kept greater than the sheet width of the rolled material in order to smoothly carry out the rolling operation, the camber occurs on the rolled material to an extent corresponding to this margin.
After all, it can be concluded that the problems of the prior art technologies described above result from the absence of the method that can measure and control very accurately and without a time delay the camber that occurs owing to various causes.
It is therefore an object of the invention to provide a rolling method for a flat-rolled metal material and a rolling apparatus for the method that can advantageously solve the problems of the prior art technologies, regarding the camber control described above, and can stably produce a flat-rolled metal material not having, or having extremely light, camber.